U.S. patent number 11,046,787 [Application Number 16/612,552] was granted by the patent office on 2021-06-29 for polylactide-grafted cellulose nanofiber and production method thereof.
This patent grant is currently assigned to DAIO PAPER CORPORATION, OSAKA RESEARCH INSTITUTE OF INDUSTRIAL SCIENCE AND TECHNOLOGY. The grantee listed for this patent is DAIO PAPER CORPORATION, OSAKA RESEARCH INSTITUTE OF INDUSTRIAL SCIENCE AND TECHNOLOGY. Invention is credited to Yasuyuki Agari, Hiroshi Hirano, Takaaki Imai, Joji Kadota, Akinori Okada.
United States Patent |
11,046,787 |
Kadota , et al. |
June 29, 2021 |
Polylactide-grafted cellulose nanofiber and production method
thereof
Abstract
Provided are a polylactide-grafted cellulose nanofiber that is
suitable as a molding material, and a production method thereof. A
polylactide-grafted cellulose nanofiber includes grafted cellulose
having a graft chain bonding to cellulose constituting a cellulose
nanofiber, wherein the graft chain is a polylactide, and a ratio of
an absorbance derived from C.dbd.O of the polylactide to an
absorbance derived from O--H of the cellulose on an infrared
absorption spectrum is no less than 0.01 and no greater than 1,000.
In addition, a production method of a polylactide-grafted cellulose
nanofiber includes carrying out graft polymerization of a lactide
to cellulose constituting a cellulose nanofiber in the presence of
an organic polymerization catalyst which includes an amine and a
salt obtained by reacting the amine with an acid. As the organic
polymerization catalyst, 4-dimethylaminopyridine and
4-dimethylaminopyridinium triflate are preferred.
Inventors: |
Kadota; Joji (Osaka,
JP), Agari; Yasuyuki (Osaka, JP), Hirano;
Hiroshi (Osaka, JP), Okada; Akinori (Osaka,
JP), Imai; Takaaki (Shikokuchuo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
OSAKA RESEARCH INSTITUTE OF INDUSTRIAL SCIENCE AND TECHNOLOGY
DAIO PAPER CORPORATION |
Izumi
Shikokuchuo |
N/A
N/A |
JP
JP |
|
|
Assignee: |
OSAKA RESEARCH INSTITUTE OF
INDUSTRIAL SCIENCE AND TECHNOLOGY (Osaka, JP)
DAIO PAPER CORPORATION (Ehime, JP)
|
Family
ID: |
1000005646425 |
Appl.
No.: |
16/612,552 |
Filed: |
May 9, 2018 |
PCT
Filed: |
May 09, 2018 |
PCT No.: |
PCT/JP2018/018017 |
371(c)(1),(2),(4) Date: |
November 11, 2019 |
PCT
Pub. No.: |
WO2018/207848 |
PCT
Pub. Date: |
November 15, 2018 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20200123275 A1 |
Apr 23, 2020 |
|
Foreign Application Priority Data
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|
|
|
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May 12, 2017 [JP] |
|
|
JP2017-095975 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08K
5/3432 (20130101); C08G 63/08 (20130101); C08B
15/00 (20130101) |
Current International
Class: |
C08B
15/00 (20060101); C08K 5/3432 (20060101); C08G
63/08 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101168616 |
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Apr 2008 |
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CN |
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62-240066 |
|
Oct 1987 |
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JP |
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2004-359840 |
|
Dec 2004 |
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JP |
|
2005-35134 |
|
Feb 2005 |
|
JP |
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2007-536426 |
|
Dec 2007 |
|
JP |
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2011-252102 |
|
Dec 2011 |
|
JP |
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2013-519736 |
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May 2013 |
|
JP |
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5545985 |
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Jul 2014 |
|
JP |
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2006/001076 |
|
Jan 2006 |
|
WO |
|
2008/143322 |
|
Nov 2008 |
|
WO |
|
Other References
International Search Report dated Jul. 17, 2018, issued in
counterpart International Application No. PCT/JP2018/018017 (2
pages). cited by applicant .
Extended Search Reported dated Nov. 5, 2020, issued in counterpart
EP Application No. 18798416.6 (6 pages). cited by
applicant.
|
Primary Examiner: Salamon; Peter A
Attorney, Agent or Firm: Westerman, Hattori, Daniels &
Adrian, LLP
Claims
The invention claimed is:
1. A polylactide-grafted cellulose nanofiber comprising grafted
cellulose which comprises a graft chain bonding to cellulose
constituting a cellulose nanofiber, wherein the graft chain is a
polylactide, a ratio of an absorbance derived from C.dbd.O of the
polylactide to an absorbance derived from O--H of the cellulose on
an infrared absorption spectrum is no less than 0.01 and no greater
than 1,000, the cellulose nanofiber has a width of no less than 1
nm and no greater than 1,000 nm, the cellulose nanofiber has a
degree of crystallization of no less than 20% and no greater than
90%, and the polylactide is selected from the group consisting of a
polymer of L-lactide, a polymer of D-lactide, and a random or block
copolymer of L-lactide and D-lactide.
2. A production method of a polylactide-grafted cellulose nanofiber
of claim 1 comprising carrying out graft polymerization of a
lactide to cellulose constituting a cellulose nanofiber in the
presence of an organic polymerization catalyst which comprises an
amine and a salt obtained by reacting the amine with an acid.
3. The production method of a polylactide-grafted cellulose
nanofiber according to claim 2, wherein the organic polymerization
catalyst is 4-dimethylaminopyridine and 4-dimethylaminopyridinium
triflate.
4. The production method of a polylactide-grafted cellulose
nanofiber according to claim 2, wherein the graft polymerization is
repeated multiple times.
5. The production method of a polylactide-grafted cellulose
nanofiber according to claim 3, wherein the graft polymerization is
repeated multiple times.
Description
TECHNICAL FIELD
The present invention relates to a polylactide-grafted cellulose
nanofiber and a production method thereof.
BACKGROUND ART
In recent years, from the perspective of conservation of global
environment, biodegradable polymers that can be decomposed in
natural environment due to actions of microorganisms existing in
soil and water have attracted attention, and a variety of
biodegradable polymers are developed. A typical example of the
biodegradable polymer is a polylactide. The polylactide is
characterized by comparatively low cost, and is expected as a
biodegradable polymer that is melt moldable. In addition,
production of a lactide that is a starting monomer of the
polylactide at low cost has been enabled recently by a fermentation
process in which a microorganism is used, thereby enabling the
polylactide to be produced at an even further low cost, and thus
use thereof as not only a biodegradable polymer but also a
multipurpose polymer has been investigated.
On the other hand, although the polylactide has superior
characteristics among the biodegradable polymers, due to having
properties of being rigid and comparatively fragile as well as
poorly flexible, compared with multipurpose polymers, it is
necessary to add a softening agent in cases of manufacturing a
molded product using the polylactide as a raw material. In
addition, the polylactide has still insufficient heat resistance,
and somewhat lacks in microwave-oven resistance. Furthermore, the
polylactide also has properties of insufficient melting
characteristics required in extrusion molding as well as blow
molding and expansion molding.
In this regard, a technique of obtaining a resin composition
superior in color tone and mechanical characteristics by melt
kneading of a polylactide resin and a naturally-occurring organic
filler under a specific condition is disclosed (see Japanese
Unexamined Patent Application, Publication No. 2005-35134).
PRIOR ART DOCUMENTS
Patent Documents
Patent Document 1: Japanese Unexamined Patent Application,
Publication No. 2005-35134
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
However, such a naturally-occurring organic filler as in the prior
art described above is likely to have a hydrophilic surface, and
thus tends to be inferior in dispersibility into a molding resin
that is highly hydrophobic. Furthermore, in a case in which
mechanical strength such as a flexural property is improved,
toughness and flexibility may be impaired. Therefore, the molding
material should have favorable strength and flexibility and should
essentially enable the filler surface to be hydrophobilized in
manufacturing a molded product, and thus various surface
hydrophobilization treatments have been attempted. Additionally,
mere surface hydrophobilization is hardly effective when shearing
force is generated between the filler surface and the molding
resin. Therefore, for imparting sufficient mechanical properties,
strong interaction with an organic material such as a resin is
required through, for example, providing the organic filler having
a sufficiently long organic molecular chain.
The present invention was made in view of the foregoing
circumstances, and an object of the invention is to provide a
polylactide-grafted cellulose nanofiber that is suitable as a
molding material, and a production method thereof.
Means for Solving the Problems
According to an aspect of the invention made for solving the
aforementioned problems, a polylactide-grafted cellulose nanofiber
includes grafted cellulose having a graft chain bonding to
cellulose constituting a cellulose nanofiber, wherein the graft
chain is a polylactide, and a ratio of an absorbance derived from
C.dbd.O of the polylactide to an absorbance derived from O--H of
the cellulose on an infrared absorption spectrum is no less than
0.01 and no greater than 1,000.
The polylactide-grafted cellulose nanofiber includes grafted
cellulose, in which a graft chain bonding to the cellulose is a
polylactide. Since the ratio of the absorbance derived from C.dbd.O
of the carbonyl group included in the polylactide to an absorbance
derived from O--H of the hydroxyl group included in cellulose on an
infrared absorption spectrum is no less than 0.01 and no greater
than 1,000, suitable performances as a molding material can be
obtained in addition to biodegradability and rigidity of the
polylactide. Moreover, in addition to use as a molding material
alone, the polylactide-grafted cellulose nanofiber enables a
suitable performance to be attained also as a surface-modified
organic additive. The "cellulose nanofiber" as referred to herein
means a fine cellulose fiber that can be obtained by defibration of
a biomass such as pulp fibers, and in general, means a cellulose
fiber that includes cellulose fine fibers having a width of nano
size (no less than 1 mm and no greater than 1,000 mm).
According to other aspect of the present invention made for solving
the aforementioned problems, a production method of a
polylactide-grafted cellulose nanofiber includes carrying out graft
polymerization of a lactide to cellulose constituting a cellulose
nanofiber in the presence of an organic polymerization catalyst
which includes an amine and a salt obtained by reacting the amine
with an acid.
In the production method of a polylactide-grafted cellulose
nanofiber, an organic polymerization catalyst which includes an
amine and a salt obtained by reacting the amine with an acid is
used as a catalyst for the graft polymerization. As a result, a
graft polymerization reaction of the polylactide to the cellulose
proceeds in a living polymerization manner, thereby enabling the
polylactide-grafted cellulose nanofiber to be obtained accompanied
by molecular weight distribution of the polylactide with a sharp
pattern.
As the organic polymerization catalyst, 4-dimethylaminopyridine and
4-dimethylaminopyridinium triflate are preferred. When
4-dimethylaminopyridine and 4-dimethylaminopyridinium triflate are
used as the organic polymerization catalyst, the graft
polymerization reaction of the polylactide to the cellulose
described above can be more promoted.
In the production method of a polylactide-grafted cellulose
nanofiber, the graft polymerization is preferably repeated multiple
times. Through the graft polymerization repeated multiple times,
the production method of a polylactide-grafted cellulose nanofiber
enables the graft polymerization reaction of the polylactide to the
cellulose nanofiber to proceed efficiently, and therefore mass
productivity of the polylactide-grafted cellulose nanofiber is more
improved.
Effects of the Invention
The polylactide-grafted cellulose nanofiber and the production
method of the aspects of the present invention enable a
polylactide-grafted cellulose nanofiber that is suitable as a
molding material and a surface-modified organic additive material
to be obtained.
DESCRIPTION OF EMBODIMENTS
Hereinafter, the polylactide-grafted cellulose nanofiber and a
production method thereof according to embodiments of the present
invention are described in detail.
Polylactide-Grafted Cellulose Nanofiber
The polylactide-grafted cellulose nanofiber includes grafted
cellulose having a graft chain bonding to cellulose constituting a
cellulose nanofiber, in which the graft chain is a polylactide.
Moreover, a ratio of the absorbance derived from C.dbd.O of the
carbonyl group included in the polylactide to an absorbance derived
from O--H of the hydroxyl group included in cellulose on an
infrared absorption spectrum of the polylactide-grafted cellulose
nanofiber is no less than 0.01 and no greater than 1,000.
Cellulose Nanofiber
The cellulose nanofiber (hereinafter, may be also referred to as
"CNF") is a fiber that includes fine fibers obtained by subjecting
a biomass such as pulp fibers that include cellulose to a chemical
or mechanical treatment. As a production method of the cellulose
nanofiber, there exist options in which cellulose per se is
modified, and in which cellulose is not modified. In exemplary
methods in which cellulose per se is modified, a part of hydroxyl
groups of cellulose is modified to a carboxy group, a phosphoric
acid ester group, etc. Of these, the method in which cellulose per
se is not modified is preferred, and the reason therefor may be
inferred as in the following, for example. In a polymerization
reaction for a polylactide, a hydroxyl group serves as a starting
point, whereas a carboxy group serves as a termination point. Since
a cellulose nanofiber is used as an initiator for the
polylactide-grafted cellulose nanofiber, a hydroxyl group of the
cellulose nanofiber serves as the starting point of the reaction.
Therefore, in the case in which a part of the hydroxyl groups of
the cellulose is modified to a carboxy group, a phosphoric acid
ester group, etc., the starting points of the graft polymerization
reaction of the polylactide decrease, and thus the cellulose
nanofiber not having been chemically modified is preferably used.
The cellulose nanofiber not having been chemically modified is
exemplified by a cellulose nanofiber microfabricated by a
mechanical treatment. The modification amount of the hydroxyl
groups of the cellulose nanofiber obtained is preferably no greater
than 0.5 mmol/g, more preferably no greater than 0.3 mmol/g, and
still more preferably no greater than 0.1 mmol/g.
Examples of the Pulp Fiber Include:
chemical pulp, e.g., hardwood kraft pulp (LKP) such as hardwood
bleached kraft pulp (LBKP) and hardwood unbleached kraft pulp
(LUKP), needle-leaved kraft pulps (NKP) such as needle-leaved
bleached kraft pulp (NBKP) and needle-leaved unbleached kraft pulp
(NUKP), and the like;
mechanical pulps such as stone-ground pulp (SGP), pressurized
stone-ground pulp (PGW), refiner-ground pulp (RGP), chemi-ground
pulp (CGP), thermo-ground pulp (TGP), ground pulp (GP),
thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP) and
bleached thermomechanical pulp (BTMP).
Of these, bleached chemical pulp (LBKP, NBKP) is preferably used
which contains as a principal component, cellulose having a large
number of hydroxyl groups that serve as starting points of the
reaction of polymerization for the polylactide.
Prior to microfabrication by a mechanical treatment of the pulp
fiber in a slurry, a chemical or mechanical pretreatment may be
carried out in an aqueous system. The pretreatment is carried out
for reducing the energy for mechanical defibration in the
microfabrication step which will follow. The pretreatment is not
particularly limited as long as a procedure for the pretreatment is
employed in which modification of a functional group of cellulose
of the cellulose nanofiber is not caused, and the reaction in an
aqueous system enabled. As described above, the cellulose nanofiber
is preferably produced by a method in which the functional group of
cellulose is not modified. For example, there exists a method in
which a primary hydroxyl group of cellulose is preferentially
oxidized by using a treatment agent in the chemical pretreatment of
the pulp fiber in the slurry, with an N-oxyl compound such as a
2,2,6,6-tetramethyl-1-piperidine-N-oxy (TEMPO) radical as a
catalyst, as well as a method in which a phosphoric acid-based
chemical is used to modify the hydroxyl group with a phosphoric
acid ester group. However, according to these methods, defibration
to a level of single nano order (several nm) fiber diameter occurs
at once when the mechanical defibration is conducted, and thus
carrying out a miniaturization treatment may be difficult to meet a
desired fiber size. Furthermore, it is considered that by
decreasing the hydroxyl group that serves as the starting point of
the reaction as described above, the polymerization reaction of the
polylactide may be difficult to proceed. Therefore, a production
method is desired in which mechanical defibration is carried out in
combination with a mild chemical treatment not leading to
modification of the hydroxyl group of cellulose, such as hydrolysis
using, for example, a mineral acid (hydrochloric acid, sulfuric
acid, phosphoric acid, etc.), an enzyme or the like. By adjusting
degrees of the chemical pretreatment and the mechanical
defibration, the miniaturization treatment can be carried out to
meet a desired fiber size. In addition, by carrying out a
pretreatment in an aqueous system, cost for recovery and/or
elimination of the solvent can be reduced. The pretreatment may be
carried out in concurrence with the chemical pretreatment, or in
combination with the mechanical pretreatment (defibration
treatment).
The cellulose nanofibers exhibit a single peak on a pseudo particle
size distribution curve obtained by a measurement with a laser
diffraction method in a state of having been dispersed in water.
The particle diameter corresponding to the peak on the pseudo
particle size distribution curve (i.e., most frequently found
diameter) is preferably no less than 5 .mu.m and no greater than 60
.mu.m. In the case in which the cellulose nanofibers exhibit such
particle size distribution, favorable performances owing to
sufficient microfabrication can be achieved. It is to be noted that
"pseudo particle size distribution curve" as referred to herein
means a curve indicating particle size distribution based on the
volume as measured by using a particle size distribution measuring
equipment (for example particle size distribution analyzer of laser
diffraction scattering type, available from Seishin Enterprise Co.,
Ltd.).
Average Fiber Diameter
It is desired that the average fiber diameter of the cellulose
nanofibers is no less than 4 nm and no greater than 1,000 nm. It is
considered that through miniaturization of the fibers to the
average fiber width described above, the number of fibers in a
molten resin per weight is increased, thereby enabling contribution
to an increase in melt viscosity of the resin.
The average fiber diameter is measured by the following method.
One hundred milliliter of a dispersion liquid of the cellulose
nanofibers in water having a solid content concentration of no less
than 0.01% by mass and no greater than 0.1% by mass is filtered
through a membrane filter made of Teflon (registered trademark),
and solvent replacement is conducted with t-butanol. Next, freeze
drying is carried out and coating with a metal such as osmium gives
a sample for observation. With respect to this sample, an
observation is performed by electron microscopic SEM imaging at any
magnification of 3,000 times, 5,000 times, 10,000 times or 30,000
times, in accordance with widths of constituting fibers.
Specifically, two diagonal lines are drawn on an image for
observation, and three straight lines that pass the intersection of
the diagonal lines are arbitrarily drawn. Furthermore, widths of
100 fibers in total that cross these three straight lines are
measured by visual inspection. Then, a middle diameter of the
measurements is determined as the average fiber diameter.
Degree of Crystallization
The lower limit of the degree of crystallization of the cellulose
nanofibers is preferably 10%, more preferably 15%, and still more
preferably 20%. When the degree of crystallization is less than
10%, the strength of the fibers per se is deteriorated, and
therefore an effect of improving the melt viscosity may be
impaired.
On the other hand, the upper limit of the degree of crystallization
of the cellulose nanofibers is not particularly limited, but is
preferably no greater than 95%, and more preferably no greater than
90%. When the degree of crystallization is greater than 95%, a
proportion of strong hydrogen bonds in molecules is increased,
whereby the fibers per se can be rigid; however, it is considered
that the chemical modification of the cellulose nanofibers may be
difficult. It is to be noted that degree of crystallization is
arbitrarily adjustable by way of, for example, selection of pulp
fibers, the pretreatment, the miniaturization treatment, etc. The
degree of crystallization is a value measured by a X-ray
diffraction analysis in accordance with "general rules for X-ray
diffraction analysis" of JIS-K0131 (1996). It is to be noted that
cellulose nanofiber has amorphous parts and crystalline parts, and
the degree of crystallization means the proportion of crystalline
parts in the entirety of the cellulose nanofibers.
Pulp Viscosity
The lower limit of the pulp viscosity of the cellulose nanofiber is
preferably 0.1 cps, and more preferably 0.5 cps. When the pulp
viscosity is less than 0.1 cps, resulting from a low degree of
polymerization of the cellulose nanofibers, a fibrous state may not
be maintained during the polymerization reaction for the
polylactide, and the effect of improving the melt viscosity may be
impaired.
In addition, the upper limit of the pulp viscosity of the cellulose
nanofiber is preferably 50 cps, and more preferably 40 cps. When
the pulp viscosity is greater than 50 cps, the degree of
polymerization of the cellulose nanofiber per se is so great that
the fiber is too long, whereby sufficient inhibition of aggregation
of cellulose nanofibers may fail in the polymerization reaction for
the polylactide, and thus the polymerization reaction for the
polylactide may proceed nonuniformly. The pulp viscosity is
measured in accordance with JIS-P8215 (1998). It is to be noted
that a greater pulp viscosity indicates a greater degree of
polymerization of the cellulose.
Type B Viscosity
In the case in which a solid content concentration of the cellulose
nanofibers in the solution is 1% by mass, the lower limit of type B
viscosity of the dispersion liquid is preferably 1 cps, more
preferably 3 cps, and still more preferably 5 cps. When the type B
viscosity of the dispersion liquid is less than 1 cps, the fibrous
state may not be maintained during the polymerization reaction for
the polylactide, and the effect of improving the melt viscosity may
be impaired.
Meanwhile, the upper limit of the type B viscosity of the
dispersion liquid is preferably 7,000 cps, more preferably 6,000
cps, and still more preferably 5,000 cps. When the type B viscosity
of the dispersion liquid is greater than 7,000 cps, enormous energy
is required for pumping up for transfer of a dispersion in water,
whereby the production cost may be increased. The type B viscosity
is measured on a dispersion liquid of the cellulose nanofibers in
water having a solid content concentration of 1%, in accordance
with "methods for viscosity measurement of liquid" of JIS-Z8803
(2011). The type B viscosity is a resistance torque in stirring a
slurry, and a greater type B viscosity indicates a greater energy
being required for the stirring.
Water-Holding Capacity
The upper limit of the water-holding capacity of the cellulose
nanofiber is preferably 600%, more preferably 580%, and still more
preferably 560%. When the water-holding capacity is greater than
600%, efficiencies of solvent replacement and drying are
deteriorated, which may lead to an increase in production cost. The
water-holding capacity is arbitrarily adjustable by way of, for
example, selection of pulp fibers, the pretreatment, and the
miniaturization treatment. The water-holding capacity is measured
in accordance with JAPAN TAPPI No. 26: 2000.
Polylactide
The polylactide to be the graft chain is exemplified by a polymer
of L-lactide, a polymer of D-lactide, a random or block copolymer
of L-lactide and D-lactide, and the like.
Ratio of absorbance derived from C.dbd.O to absorbance derived from
O--H on infrared absorption spectrum
The polylactide-grafted cellulose nanofiber is insoluble in most
solvents, and is not molten even after being heated; therefore, a
structural analysis thereof through molecular weight determination
by a GPC process or determination on NMR is impossible. Thus, by
way of the measurement of an infrared ray absorption (hereinafter,
may be also referred to as IR) spectrum, a ratio of an absorbance
derived from C.dbd.O of the polylactide to an absorbance derived
from O--H of the cellulose (hereinafter, may be also merely
referred to as "absorbency ratio") of the polylactide-grafted
cellulose nanofiber is determined, and used as a marker of the
degree of grafting. The absorbency ratio is determined by measuring
the IR spectrum after purifying the polylactide-grafted cellulose
nanofiber with a solvent such as dichloromethane and
tetrahydrofuran that is capable of dissolving the polylactide to
completely eliminate the polylactide not being grafted. The lower
limit of the ratio of the absorbance derived from C.dbd.O of the
polylactide to the absorbance derived from O--H of the cellulose on
the IR spectrum of the polylactide-grafted cellulose nanofiber is
typically 0.01, and more preferably 0.05. The absorbency ratio
being less than 0.01 is not preferred since characteristics as the
polylactide are less likely to be exhibited. The upper limit of the
absorbency ratio may be typically 1,000, and more preferably 300.
When the absorbency ratio is greater than 1,000, characteristics of
cellulose are tend to be hardly found.
The polylactide-grafted cellulose nanofiber is suitable as a
biodegradable molding material, and as an additive of a molding
material. Therefore, the polylactide-grafted cellulose nanofiber
can be used: for processing to provide various types of molded
products by a procedure such as injection molding, extrusion
molding or blow molding; and as an additive of a resinous material
such as a polylactide.
In addition, with respect to the intended usage, the
polylactide-grafted cellulose nanofiber and the molding material to
which the fiber is added may be used not only as an injection
molded product such as a vessel, but also as a compression molded
product, an extrusion molded product, a blow molded product or the
like, in the form of a sheet, a film, a foamed material, fibers and
the like. These molded products may be utilized for intended usage
such as electronic parts, building components, civil engineering
components, agricultural materials, automobile parts, daily
necessities, and the like. In addition, the polylactide-grafted
cellulose nanofiber may be used not only as an organic filler but
also as an additive for improving performances of various types of
materials, such as a nucleating agent, a crystallization
retardation agent, a foamed material improving agent, a film
improving agent, and the tike. Furthermore, the polylactide-grafted
cellulose nanofiber may be also used as a biodegradable
adhesive.
Production Method of Polylactide-Grafted Cellulose Nanofiber
Next, the production method of a polylactide-grafted cellulose
nanofiber is described. According to the production method of a
polylactide-grafted cellulose nanofiber, graft polymerization of a
lactide to cellulose constituting a cellulose nanofiber is carried
out in the presence of an organic polymerization catalyst to
provide a polylactide-grafted cellulose nanofiber. More
specifically, the production method of a polylactide-grafted
cellulose nanofiber includes a step of carrying out graft
polymerization of a lactide to the aforementioned cellulose having
a hydroxyl group, in the presence of an organic polymerization
catalyst which includes an amine and a salt obtained by reacting
the amine with an acid. In the graft polymerization step, a
ring-opened lactide is polymerized via an ester bond to each
hydroxyl group of the cellulose constituting the cellulose
nanofiber in the presence of the organic polymerization catalyst to
give the polylactide as a graft chain.
According to the production method of a polylactide-grafted
cellulose nanofiber, since the organic polymerization catalyst
includes an amine and a salt obtained by reacting the amine with an
acid, the graft polymerization reaction of the polylactide to the
cellulose proceeds in a living polymerization manner, thereby
enabling the polylactide-grafted cellulose nanofiber to be obtained
accompanied by molecular weight distribution of the polylactide
with a sharp pattern.
Examples of the amine in the organic polymerization catalyst
include: alkylamines such aa methylamine, triethylamine and
ethylenediamine; aromatic amines such as aniline; heterocyclic
amines such as pyrrolidine, imidazole and pyridine; amine
derivatives such as an ether amine and an amino acid; and the like.
Of these, 4-dimethylaminopyridine is preferred from the viewpoint
of enabling the graft polymerization reaction of the polylactide to
cellulose constituting a cellulose nanofiber to be more
promoted.
Examples of the acid in the organic polymerization catalyst
include: inorganic acids such as hydrochloric acid; sulfonic acids
such as p-toluenesulfonic acid and trifluoromethanesulfonic acid:
carboxylic acids such as acetic acid; and the like. With respect to
the acid, since higher acidity leads to a greater catalytic
activity, p-toluenesulfonic acid and trifluoromethanesulfonic acid
are preferred among the acids exemplified above, and of these,
trifluoromethanesulfonic acid is more preferred.
Examples of the salt obtained by reacting the amine with the acid
in the organic polymerization catalyst include
4-dimethylaminopyridinium triflate, 4-dimethylaminopyridinium
tosylate, 4-dimethylaminopyridinium chloride, and the like. Of
these, in tight of a capability of more promoting the graft
polymerization reaction for the polylactide to cellulose
constituting the cellulose nanofiber, 4-dimethylaminopyridinium
triflate is preferred.
By using 4-dimethylaminopyridine and 4-dimethylaminopyridinium
triflate as the organic polymerization catalyst in the production
method of a polylactide-grafted cellulose nanofiber, the effect of
more promoting the graft polymerization reaction for the
polylactide to the cellulose nanofiber can be further enhanced.
The polylactide-grafted cellulose nanofiber can be synthesized
according to the following scheme, for example.
##STR00001##
In the above scheme, n and m are each an integer of no less than 1.
As described above, L-lactide, D-lactide or a combination thereof
may be used as the lactide. The form of the polymer which may be
adopted involves: L-polylactide or D-polylactide each obtained when
L-lactide or D-lactide is used alone; a random copolymer in which
the sequence order of L-lactide and D-lactide is random, which is
obtained when L-lactide and D-lactide are used in combination; and
a block copolymer in which L-lactide and D-lactide are polymerized
block-wise in an arbitrary proportion.
In the production method of a polylactide-grafted cellulose
nanofiber, it is preferred that the graft polymerization step is
repeated multiple times in a case in which the grafting percentage
is to be increased. By repeating the graft polymerization step
multiple times, the graft polymerization reaction for the
polylactide to the cellulose nanofiber can efficiently proceed,
whereby the mass productivity of the polylactide-grafted cellulose
nanofiber is more improved. For example, by repeating the graft
polymerization step twice, the polylactide-grafted cellulose
nanofiber can be efficiently produced, with the ratio of an
absorbance derived from C.dbd.O of the polylactide to an absorbance
derived from O--H of the cellulose on the IR spectrum of the
polylactide-grafted cellulose nanofiber being no less than 0.01 and
no greater than 1,000. When a further increase in the grafting
percentage is intended, repeating the step necessary times is also
possible.
After the polylactide-grafted cellulose nanofiber is obtained by
the graft polymerization step, the polylactide not being grafted
(ungrafted polylactide) is also included. The polylactide-grafted
cellulose nanofiber may be used in the state of including the
ungrafted polylactide; however, in order to more exert the
characteristics of the polylactide-grafted cellulose nanofiber, it
is preferred that the production method further includes a
purification step for completely eliminating the ungrafted
polylactide. A solvent for use in the purification step is not
particularly limited as long as the polylactide is dissolved, and
dichloromethane, tetrahydrofuran or a combination thereof is
preferably used.
According to the production method of a polylactide-grafted
cellulose nanofiber, the polylactide-grafted cellulose nanofiber
that is biodegradable and suitable as both a molding material and a
surface-modified organic additive material can be certainly
produced.
Other Embodiments
The present invention is not limited to the embodiments described
above, and may be put into practice in not only the above modes but
in modes having been variously altered and/or modified.
EXAMPLES
Hereinafter, the present invention is mote specifically described
by way of Examples, but the present invention is not limited to the
following Examples.
Ratio of Absorbance Derived from C.dbd.O to Absorbance Derived from
O--H on IR Spectrum
The ratio of an absorbance derived from C.dbd.O of the polylactide
to an absorbance derived from O--H of the cellulose on an IR
spectrum was determined. The peak intensity on the IR spectrum was
measured under the following conditions.
IR measurement conditions apparatus: Fourier transform infrared
spectrometer FT-IR6700 manufactured by Nicolet and DURASCOPE
manufactured by SeusIR Technologies
optical resolution: 4 cm.sup.-1
integration count: 32
measuring method: ATR method
measurement absorbance: O--H deriving peak: around 3,680 cm.sup.-1
to 3,000 cm.sup.-1 C.dbd.O deriving peak: around 1,890 cm.sup.-1 to
1,520 cm.sup.-1
Differential Scanning Calorimetry (DSC)
Measurement of the glass transition temperature, the
crystallization temperature, and the heat for melting was performed
by a DSC method under the conditions below. It is to be noted that
the data presented in Table 3 below show results obtained in course
(3) in the following temperature program (for one measurement,
temperature up and temperature down were executed in the order of
(1), (2), (3) below).
apparatus: EXSTAR DSC6200, manufactured by Hitachi
High-Technologies Corporation
nitrogen flow rate: 40 ml/min.
temperature up and cooling conditions: temperature up and
temperature down being executed continuously in the order of (1),
(2), (3). rate of temperature up and temperature down: 10.degree.
C./min. (1) 10.degree. C. to 200.degree. C. (2) 200.degree. C. to
10.degree. C. (3) 10.degree. C. to 200.degree. C.
standard substance: alumina powder
sample container: open aluminum pan
sample mass: about 5 mg
One-Step Graft Polymerization
Example 1
(1) Synthesis of 4-Dimethylaminopyridinium Triflate being a
Polymerization Catalyst
In a two-neck flask (volume: 100 ml), 1.22 g of
4-dimethylaminopyridine (manufactured by Tokyo Chemical Industry
Co., Ltd., white powder) was dissolved in 20 ml of tetrahydrofuran
in a dry nitrogen atmosphere. Subsequently, 1.50 g of
trifluoromethanesulfonic acid was added dropwise and the mixture
was stirred while the two-neck flask was cooled in a ice-cooling
bath at 0.degree. C. Thereafter, the temperature was allowed to be
the room temperature, and the stirring was continued for 1 hour.
The reaction mixture was filtered through a glass filter, washed
with 10 ml of tetrahydrofuran twice, and then dried under reduced
pressure to give quantitatively 4-dimethylaminopyridinium triflate
as white powder.
(2) Preparation of Dry Cellulose Nanofiber
A raw material pulp (LBKP, solid content: 2% by mass) was subjected
to a pretreatment with a beater for paper making, and thereafter a
miniaturization treatment was carried out by using a high-pressure
homogenizer to a level of having a single peak in pseudo particle
size distribution by a particle size distribution measurement
through using laser diffraction (most frequently found diameter: 30
.mu.m), whereby a dispersion of cellulose nanofiber (hereinafter,
referred to as "CNF") in water having a solid content of 2% by mass
was produced. After the CNF dispersion in water was subjected to a
centrifugal separator, the supernatant liquid was eliminated, a
solvent was added thereto, followed by homogenization and
centrifugal separation again to permit concentration. This
operation was repeated several times followed by freeze drying to
remove the solvent. Accordingly, CNF was prepared as white
powder.
(3) Grafting of Polylactide to CNF
Into a two-neck flask (volume: 50 ml), 54 mg of CNF white powder,
6.1 mg (0.05 mmol) of 4-dimethylaminopyridine (manufactured by
Tokyo Chemical Industry Co., Ltd.) white powder, 13.6 mg (0.05
mmol) of 4-dimethylaminopyridinium triflate synthesized as
described above, and 720 mg (5 mmol) of colorless and transparent
rod-shape crystalline L-lactide were added in a dry-nitrogen
atmosphere. The two-neck flask was then heated in an oil bath at
100.degree. C. for 1 hour to give a colorless and transparent
solid.
(4) Purification of Polylactide-Grafted CNF
The colorless and transparent solid thus obtained was dissolved in
10 ml of dichloromethane, and the insoluble matter was recovered by
filtration on a glass filter. To the filter residue, 20 mL of
tetrahydrofuran was added, and subjected to a centrifugal separator
(H-200, manufactured by KOKUSAN Co. Ltd., at 5,000 rpm for 15 min).
Thereafter, the supernatant was removed, and 20 mL of
tetrahydrofuran was added again and the mixture was subjected to
the centrifugal separator by a similar operation followed by
removing of the supernatant. Thus, ungrafted polylactide was
eliminated to give 52 mg of polylactide-grafted CNF. The ratio of
the absorbance derived from C.dbd.O to the absorbance derived from
O--H on the IR spectrum in the polylactide-grafted CNF thus
obtained was 0.8.
Example 2
Polylactide-grafted CNF was obtained in a similar manner to Example
1 except that the amount of CNF used was changed to 41 mg. The
ratio of the absorbance derived from C.dbd.O to the absorbance
derived from O--H on the IR spectrum in the polylactide-grafted CNF
thus obtained was 2.8. The glass transition temperature of the
polylactide-grafted CNF of Example 2 was 51.1.degree. C.
Example 3
Polylactide-grafted CNF was obtained in a similar manner to Example
1 except that the amount of CNF used was changed to 27 mg. The
ratio of the absorbance derived from C.dbd.O to the absorbance
derived from O--H on the IR spectrum in the polylactide-grafted CNF
thus obtained was 5.8. The glass transition temperature of the
polylactide-grafted CNF of Example 3 was 51.6.degree. C.
Example 4
Polylactide-grafted CNF was obtained in a similar manner to Example
1 except that the amount of CNF used was changed to 14 mg. The
ratio of the absorbance derived from C.dbd.O to the absorbance
derived from O--H on the IR spectrum in the polylactide-grafted CNF
thus obtained was 7.1. The glass transition temperature of the
polylactide-grafted CNF of Example 4 was 51.2.degree. C.
Example 5
Polylactide-grafted CNF was obtained in a similar manner to Example
1 except that the amount of CNF used was changed to 5 mg. The ratio
of the absorbance derived from C.dbd.O to the absorbance derived
from O--H on the IR spectrum in the polylactide-grafted CNF thus
obtained was 3.3.
Table 1 shows ratios of the absorbance derived from C.dbd.O to the
absorbance derived from O--H on IR spectra of Examples 1 to 5, and
glass transition temperatures. Additionally, the glass transition
temperature of CNF alone is shown together in Table 1 as Reference
Example 1.
TABLE-US-00001 TABLE 1 Ratio of absorbance Glass derived from
C.dbd.O to transition CNF Polylactide-grafted CNF absorbance
derived from temperature used (mg) obtained (mg) O--H on IR
spectrum (.degree. C.) Example 1 54 52 0.8 -- Example 2 41 39 2.8
51.1 Example 3 27 27 5.8 51.6 Example 4 14 11 7.1 51.2 Example 5 5
5 3.3 -- Referenee -- -- -- not detected Example 1 (CNF alone)
Two-Step Graft Polymerization
Example 6
(1) Grafting of Polylactide to Polylactide-Grafted CNF in Second
Step
Into a two-neck flask (volume: 50 ml), 5 mg of the
polylactide-grafted CNF of Example 1, 6.1 mg (0.05 mmol) of white
powder of 4-dimethylaminopyridine (manufactured by Tokyo Chemical
Industry Co., Ltd.), 13.6 mg (0.05 mmol) of
4-dimethylaminopyridinium triflate, and 720 mg (5 mmol) of
colorless and transparent rod-shaped crystals of lactide were added
in a dry-nitrogen atmosphere. The two-neck flask was then heated in
an oil bath at 100.degree. C. for 1 hour to give a colorless and
transparent solid.
(2) Purification of Polylactide-Grafted CNF after Graft
Polymerization in Second Step
The colorless and transparent solid thus obtained was dissolved in
10 ml of dichloromethane, and the insoluble matter was recovered by
filtration on a glass filter. To the filter residue, 20 mL of
tetrahydrofuran was added, and subjected to a centrifugal separator
(H-200, manufactured by KOKUSAN Co. Ltd., at 5,000 rpm for 15 min).
Thereafter, the supernatant was removed, and 20 mL of
tetrahydrofuran was added again and the mixture was subjected to
the centrifugal separator by a similar operation followed by
removing of the supernatant. Thus, ungrafted polylactide was
completely eliminated to give intended polylactide-grafted CNF (27
mg). The ratio of the absorbance derived from C.dbd.O to the
absorbance derived from O--H on the IR spectrum in the
polylactide-grafted CNF thus obtained was 11.2.
Example 7
Polylactide-grafted CNF was obtained in a similar manner to Example
6 except that 5 mg of the polylactide-grafted CNF of Example 2 was
used in place of 5 mg of the polylactide-grafted CNF of Example 1.
The ratio of the absorbance derived from C.dbd.O to the absorbance
derived from O--H on the IR spectrum in the polylactide-grafted CNF
thus obtained was 8.8.
Example 8
Polylactide-grafted CNF was obtained in a similar manner to Example
6 except that 5 mg of the polylactide-grafted CNF obtained in
Example 3 was used in place of 5 mg of the polylactide-grafted CNF
obtained in Example 1. The ratio of the absorbance derived from
C.dbd.O to the absorbance derived from O--H on the IR spectrum in
the polylactide-grafted CNF thus obtained was 6.6.
Table 2 shows the ratio of the absorbance derived from C.dbd.O to
the absorbance derived from O--H on the IR spectrum after the
grafting of the second step to the polylactide-grafted CNF.
TABLE-US-00002 TABLE 2 Mass of Ratio of polylactide- absorbance
derived grafted from C.dbd.O to Mass of CNF obtained by absorbance
derived polylactide-grafted second step of from O--H on IR CNF used
(mg) grafting (mg) spectrum Example polylactide- 5 27 11.2 6
grafted CNF of Example 1 Example polylactide- 5 11 8.8 7 grafted
CNF of Example 2 Example polylactide- 5 5 6.6 8 grafted CNF of
Example 3
Test on Crystallization Retardation Effect
One function expected for the polylactide-grafted CNF obtained
according to the present invention is a retardation or facilitation
effect on crystallization of a resin. As one example, when the
polylactide-grafted CNF is added as an additive to a commercially
available polylactide, the crystallization temperature and the heat
for melting of the commercially available polylactide may be
affected, and may in turn be expected to result in an improvement
of moldability of the resin mixture. Thus, with respect to Examples
9 to 11 below in which the polylactide-grafted CNF was mixed with a
commercially available polylactide, the crystallization temperature
and the heat for melting were determined to examine the effects on
the commercially available polylactide by adding the
polylactide-grafted CNF. The crystallization temperature and the
heat for melting were determined by a DSC method. The heat for
melting was calculated in terms of an endothermic energy amount (J)
per mass (g) of the polylactide component included in the
measurement sample. It is to be noted that as the commercially
available polylactide, a pulverized polylactide manufactured by
Osaka Gas Liquid Co., Ltd. was used.
Example 9
With 0.1 mg of the polylactide-grafted CNF obtained in Example 3,
4.98 mg of the commercially available polylactide was mixed. From
the results of DSC of Example 9, the crystallization temperature
was 129.degree. C., and the heat for melting was 0.15 J/g.
Example 10
With 0.23 mg of the polylactide-grafted CNF obtained in Example 3,
4.9 mg of the commercially available polylactide was mixed. From
the results of DSC of Example 10, the crystallization temperature
was 130.degree. C. and the heat for melting was 0.20 J/g.
Example 11
With 0.98 mg of the polylactide-grafted CNF obtained in Example 3,
4.93 mg of the commercially available polylactide was mixed. From
the results of DSC of Example 11, the crystallization temperature
was 129.degree. C. and the heat for melting was 0.21 J/g.
Comparative Example 1
The commercially available polylactide alone was employed as
Comparative Example 1. From the results of DSC of Comparative
Example 1, the crystallization temperature was 122.degree. C. and
the heat for melting was 0.97 J/g.
Comparative Example 2
Comparative Example 2 was similar to Example 9 except that 0.3 mg
of ungrafted CNF was used in place of the polylactide-grafted CNF,
and mixed with 13.4 mg of the commercially available polylactide.
From the results of DSC of Comparative Example 2, the
crystallization temperature was 121.degree. C. and the heat for
melting was 2.26 J/g.
TABLE-US-00003 TABLE 3 Mixing ratio polylactide-grafted CNF and
commercially available polylactide Percentage polylactide-
commercially content of grafted CNF ungrafted available CNF in
total Crystallization Heat for of Example 3 CNF polylactide solid
content temperature melting (mg) (mg) (mg) (% by mass) (.degree.
C.) (J/g) Example 9 0.1 -- 4.98 1.0 129 0.15 Example 10 0.23 -- 4.9
2.3 130 0.20 Example 11 0.08 -- 4.93 8.6 129 0.21 Comparative -- --
4.24 0 122 0.97 Example 1 Comparative -- 0.3 13.4 2.2 121 2.26
Example 2
As indicated by the ratios of the absorbance derived from C.dbd.O
to the absorbance derived from O--H on the IR spectra of Examples 1
to 5 shown in Table 1 above, it was suggested that carrying out the
graft polymerization of the polylactide to the cellulose nanofiber
at various grafting percentages was enabled. Moreover, as indicated
by Examples 6 to 8 shown in Table 2, the ratio of the absorbance
derived from C.dbd.O to the absorbance derived from O--H was
prominently increased by repeating the graft polymerization step
twice, revealing that efficient and significant improvement of the
grafting percentage of the polylactide was enabled.
In addition, it was indicated that the mixtures of the
polylactide-grafted CNFs of Examples 9 to 11 with the commercially
available polylactide had higher crystallization temperatures, and
required lower heat for melting than Comparative Example 1
involving the commercially available polylactide alone, and
Comparative Example 2 involving the mixture of the ungrafted CNF
with the commercially available polylactide.
INDUSTRIAL APPLICABILITY
The polylactide-grafted cellulose nanofiber of the present
invention can be suitably used as a biodegradable molding material
and a surface-modified organic additive material.
* * * * *